Due to the advancing age and high cardiovascular disease (CVD) risk of the HIV infected population, it is predicted that 78% of people living with HIV will be diagnosed with CVD by 2030. Among participants in the Women?s Interagency HIV Study (WIHS), we propose to study an extensively characterized cohort that will be extended from a women-only study to include men with and without clinical and subclinical CVD. We propose these specific aims: 1. In persons living with HIV, to address the hypothesis that specific innate and adaptive immune cell subsets will show defined transcriptomic changes associated with CVD. We have found that both HIV and CVD produce pro-inflammatory gene expression signatures in classical monocytes that partially overlap. However, human blood (PBMCs) contains at least 30 subsets of known immune cell types, which only now can be interrogated using Ab-Seq and scRNA-Seq of PBMCs. Preliminary data demonstrate feasibility. 2. To identify the expression of genes relating to tissue factor (TF) and other coagulation-related pathways in relation to HIV, CVD, inflammation, dyslipidemia and statin use. 3. To test the hypothesis that CD4+ T cells specific for the atherosclerosis antigen apolipoprotein B (APOB) lose their regulatory T cell (Treg) phenotype and to understand the mechanisms by which this promotes CVD in persons living with HIV. A critical tool is the validated tetramer reagent we use to find rare APOB-specific CD4 T cells in participants who express the DRB1*0701 allele of major histocompatibility complex (MHC)-II, comprising about 8% of all subjects. We identified 69 DRB1*0701 positive WIHS participants. The APOB-specific cells will be sorted into single wells by DRB1*0701-APOB-p18 tetramers. Deep scRNA-Seq and Ab-Seq by SMART-Seq2 will yield the first T cell receptor (TCR) sequences and matched transcriptomes for atherosclerosis-specific CD4 T cells. The proposed work has the potential to discover new targets addressable by existing or new drugs, which may improve cardiovascular outcomes in people with HIV. The project will leverage a 20+ year WIHS archive of specimens and data, new participant enrollment and CVD event collection enabled by a future commitment of NHLBI to underwrite the primary HIV cohort infrastructure support.